The major objective of this project is to study the cellular and molecular events associated with the differentiation of normal and malignant human lymphoid progenitor cells (LPC). The study will emphasize the clonal expansion of progenitor cells in non-T, non-B acute lymphoblastic leukemia (ALL), and their nonmalignant counterparts present in bone marrow (BM). Emphasis will be placed on the use of three monoclonal antibodies recently produced in our laboratory, designated BA-1, BA-2, and BA-3, that appear to bind to normal and malignant LPC at various stages of lymphoid cell development. Four specific aims have been or are being pursued: (1) A large number of lymphohematopoietic cell sources have been analyzed to determine the relationship between the aforementioned monoclonal antibodies and two intracellular markers of LPC, i.e., terminal deoxynucleotidyl transferase (TdT) and cytoplasmic IgM (CIgM). The cell populations were assayed by single or double fluorochrome staining using fluorescent microscopy and flow cytofluorimetry. The results of these studies, which identified candidate lymphoid progenitor cells, have been published. (2) The phorbol ester TPA has been used to study the induction of differentiation in normal and malignant LPC. TPA-induced changes were analyzed by immunofluorescence and biosynthetic labeling followed by SDS-PAGE. We have attempted to determine if there is a sequential (differentiation-linked?) expression of cell surface structures recognized by monoclonal antibodies and their relationship to the intracellular markers of LPC, i.e., TdT and CIgM. The results suggest that acquisition/loss of certain markers may be consistent with differentiation-linked events in lymphoid cell precursors. (3) Major emphasis is currently placed on examining the function that cell surface molecules gp40/BA-I, p24/BA-2, and gp100/CALLA/BA-3 subserve to the cells on which they are expressed. (4) Of particular interest is our recent observation that gp100/CALLA is strikingly decreased on the surface of neutrophils from patients with severe thermal injuries. Since neutrophils from these patients exhibit various dysfunctions (i.e., in hemotaxis), we are examining the possible role of gp100/CALLA in neutrophil function. (4) Studies are underway to clone the genes encoding gp40/BA-1, p24/BA-2, and gp/100/CACCA/BA-3 using mouse L cell transfection and subtractive hybridization. (LB)